Batwings (stabilizers)

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Sailor of Fortune said:
Very interesting thread, never heard of these before.
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I've seen them on many boats, mostly commercial such as trollers, but a number of pleasure boats. They are not common amongst the pleasure boats though.

There was an article in , I think Pacific Yachting, recently about the addition of a set of the long hard chine mounted types on a PT38. It was two or three months ago and they were successful, to the owner. Installed by a Coombs , B.C. yard, I think Independent Shipyards.
I don't have the mags. with me so I cannot look it up.
 
Rebel112r said:
As Dhayes said, I did have these installed. They work well, not too expensive, no downside so far.
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Thanks for those pictures, they help a lot. Now that you have had them on for a while now, was the amount of roll reduction noticeable and under what conditions? Anymore idea how much, if any, affect they have had on speed?

For a SD hull like ours, I would guess that the roll chocks would be more effective than batwings but that is just an ignorant guess.
 
Going slow in that thing would be a real drag..
 
Just guessing but I'm pretty sure that would be a hydrofoil.

Is it correct to assume the "batfish" are roughly that same size as the "fish" on para-vanes?

If so I imagine it would be at least as effective underway or anchored.
 
klee wyck said:
Thanks for that. It is as it appears then in that the roll reducing force is the lifting of the water on the top surface of one wing and the pressing of the water on the bottom surface of the other wing.
Strange that such a relatively small surface can offset that much of the roll momentum of such a large mass as the boat itself.

Very cool.
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One thing that was common to the several different batwing designs was the presence of holes in the horizontal surface. I believe this has a purpose other than to lighten the steel plate. When the vessel is rolling, some of the water going over the horizontal surface has to go through those cutouts, creating a lot of drag. I believe this drag is the predominant force in reducing the roll, as opposed to the water flowing over and around the batwing. Along the same lines, I had rolling chocks (bilge keels) fitted to a 93' steel, aft wheelhouse fishing boat, similar style as both your boats. I had holes cut out of the rolling chock allowing water to drag through while the boat was rolling, thus increasing their effectiveness.
 
I'm always looking for fresh ideas to stabilize my vessel, but at least with coastal cruisers in the Eastern US, such a design would be a trade off of reduced roll for Crab pot vulnerability. Still a nice idea though, especially if it works at anchor.
 
healhustler said:
I'm always looking for fresh ideas to stabilize my vessel, but at least with coastal cruisers in the Eastern US, such a design would be a trade off of reduced roll for Crab pot vulnerability. Still a nice idea though, especially if it works at anchor.
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I keep thinking that since I seem to ground my boat in the ICW fairly often, bad things could happen with these bat wings. Seems like they could bend, or possibly even pull away from the hull and hole the boat?
 
I don't see them as a huge issue on the Atlantic or Gulf ICW.

As far as grounding, most of the types of grounding for me a a bazillion others...you are just sliding up on mud or a sandbar if you have a keel they are bolted to.

Now backing off may be harder, but damage would only concern me if they weren't installed well or catching one on a rock somehow.

As far as crab pots, better them than my shaft....a sharp serated edge might eliminate that..,and way too many pots in the channel too....:D
 
The one I have mentioned have hit a rock. Damaged the Forward Scan Sounder. The BWs survived with a little paint loss
 
Question for Nightsky

Nightsky said:
Along the same lines, I had rolling chocks (bilge keels) fitted to a 93' steel, aft wheelhouse fishing boat, similar style as both your boats. I had holes cut out of the rolling chock allowing water to drag through while the boat was rolling, thus increasing their effectiveness.
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Guys , this is a most interesting thread as my little boat could do with some stabilization WHILE underway.
I have 'flopper stoppers' that are sensational while anchored ,so that is take care of.

Nightsky . I have continually heard rolling chocks and bilge keels mentioned in the same breath by many members. Please with respect, I know your a very knowledgeable guy, can you please clear-up this point of confusion.

What are rolling chocks and bilge keels in your opinion and are the different?

My take is:-
Flopper stoppers - hang off poles to reduce rolling while anchored NOT MOTORING.
Paravanes - hang off poles to reduce rolling while UNDERWAY
Rolling chocks - reduce rolling while UNDERWAY
Bilge keels - to sit the boat LEVEL ON THE SEABED when the tide goes out.

thx Brett
 
My take on 'real' bilge keels is two keels instead of one central keel...think of a small sailboat sitting on two keels. In the trawler version, think two stationary fins (about 20% the length of the hull?) at the turn of a full displacement hull, but not big enough to sit upright on the hard.

Rolling chocks to me are like the photo in post #23, but can be a bit closer to the keel as probably was the case with the larger commercial fishing boat in post #37.

Probably lots of local interpretation of such things, which adds to the confusion...
 
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bogranjac1 said:
Question for Nightsky



Guys , this is a most interesting thread as my little boat could do with some stabilization WHILE underway.
I have 'flopper stoppers' that are sensational while anchored ,so that is take care of.

Nightsky . I have continually heard rolling chocks and bilge keels mentioned in the same breath by many members. Please with respect, I know your a very knowledgeable guy, can you please clear-up this point of confusion.

What are rolling chocks and bilge keels in your opinion and are the different?

My take is:-
Flopper stoppers - hang off poles to reduce rolling while anchored NOT MOTORING.
Paravanes - hang off poles to reduce rolling while UNDERWAY
Rolling chocks - reduce rolling while UNDERWAY
Bilge keels - to sit the boat LEVEL ON THE SEABED when the tide goes out.

thx Brett[/QU0te

I am no expert, and I welcome being corrected by a naval architect, but the way I've always understood it, the terms rolling chocks and bilge keels have been used interchangeably (layperson will call them rolling chocks). The size and shape of the chocks (keels) is determined by their function. The chocks would be long and not stick out so far from the hull, whereas the bilge keel could extend to sit the boat level on the seabed, but I believe their attachment point on the hull would be close. My understanding has always been that paravanes, birds, stabilizers (flopper stopper) are all the same thing, just called different names based on region you live in. I have attached a photo of the chocks I had fitted to my commercial fish boat.
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Post 31, in the thread mentioned the article in Pacific Yachting magazine. It was the November 2016 issue, and was written by Rick Hudson. His experience, pretty much sums up my own. The NP does not have the corkscrewing issues that his boat does. I have noticed, no reduction of speed or increase either. There may be a couple of tenths one way or the other. It has not been an issue. The stern wave that was generated at hull speed and higher, and started 6-8 ft forward of the stern is gone. The fins trap that water. My opinion is that, that water is trapped and probably creates some stern lift which would help in slowing or tempering pitch. We left for our Alaska trip, 100 days gone right after installation. I am happy with the fins. They do not stop roll, they resist rolling and slow down the roll. In certain conditions they will trap air and slap. The ride is much better. I have not heard any negative reports from other NP owners. I have talked to 3 others. There are I think, 6 NP's that have added the fins.. Happy New Year to all!!
 
My boat looks like it would be a perfect candidate for the batwings and this is the first I have ever heard of them.
I was going to put paravanes on and I still could at a later date but am now thinking when she goes on the slip in march I will fit batwings.
Google is not telling me much on the dimensions needed to be effective, has anyone got any advice on what I may need?
I am thinking 2.4m (8 feet) Wide keeping it about 20 cm inside the boat and maybe 3m (10 feet) long and using either 12mm or 16mm plate.
She is 65 feet long and about 90t.
Any advice is welcome.
Cheers
 

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Found this old wooden hulled commercial fishing boat on the hard in Shearwater, BC. The batwings were mounted 'inelegantly' instead of against the hull under the waterline.

Pondering batwings in the flesh for a while it dawned on me that paravanes have a weak side nobody seems to mention. Since so much metal (in the way of poles and support structure for the pilothouse roof) is mounted high above the waterline, a good percentage of the paravanes roll suppressing abilities must be wasted on counteracting the additional roll produced by all that extra weight up high.

Put another way; all the weight up high must make boats that have paravanes really roll when they aren't deployed, as compared to when the same boat didn't have paravanes at all.

That's why these batwings seem to make so much sense...while they might not be as effective as paravanes when the roll reduction numbers are crunched, they don't have to be...and they are ready all the time.
 

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MurrayM said:
... Since so much metal (in the way of poles and support structure for the pilothouse roof) is mounted so high above the waterline, a good percentage of the paravanes roll suppressing abilities must be wasted on counteracting the additional roll produced by all that extra weight up high.

Put another way; all the weight up high must make boats that have paravanes really roll when they aren't deployed, as compared to when the same boat didn't have paravanes at all...
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Murray: You're right. When we first bought Hobo and were traveling in flat water, we left the poles in the vertical position. The ride seemed ok but we didn't have anything to compare it to. We later traveled with the poles deployed but with the fish out of the water, what a difference. The roll was reduced significantly. Having 2-20' sections of 2.5" schedule 80 aluminum plus the aframe was enough to affect the amount of roll even though there wasn't that much added weight. Now when ever we leave the harbor and are in open water, the poles are out even if the fish aren't deployed until we arrive at our destination.
 
Nordhavn suggest that the additional weight of a tender up high slows the roll.
A mate with a 20 ft tender with a 115hp on his 65 after says its stiffer.
A sailing yacht , sails down, that loses a mast rolls faster/more than one with a mast.

Think metronome, move weight low it beats fast, move weight high it slows down.
It is a balance, go to high and it falls over and stays there.
 
Simi 60 said:
Nordhavn suggest that the additional weight of a tender up high slows the roll.
A mate with a 20 ft tender with a 115hp on his 65 after says its stiffer.
A sailing yacht , sails down, that loses a mast rolls faster/more than one with a mast.

Think metronome, move weight low it beats fast, move weight high it slows down.
It is a balance, go to high and it falls over and stays there.
Click to expand...

Maybe the added weight high up would slow the roll period but I'll stick with my navel gazing summation that it would also increase the amount of roll, and that a certain percentage of the paravanes effectiveness would be in neutralizing that extra roll.
 
People reckon ours must roll a lot with the extra level.
I argue that when she was a commercial trawler she was designed to carry several ton of steel framework up high and now it has gone, like a yacht without a mast, she needs come extra up top to get back to where she was in the original design.

Saying that, I am looking at making some flopper stoppers - not paravanes for the rare occasion where an anchorage gets a bit wobbly.
And to keep them down to scare off close anchorers. ;)

Aluminium, not steel, so no real extra weight.
 
Batwing crab pot catchers

It looks like the batwings are made to snare crab pots...

If the leading edge were a little more of a delta wing, it might be able to shed any crab / lobster pots one encountered. They might also have to be farther aft to keep the lines from getting caught in the prop.

Other than that, sounds like a good idea.
 
"I'll stick with my navel gazing summation that it would also increase the amount of roll"

With in reason the amount of roll is not the problem, how the boat checks , switched from rolling left to right is the problem.

Boats with soft round bilges usually have the best slow stop and go , hard chines (a box ) the worst except for Cats which snap back and can become vomitoriums.

Seakindly is as much of an art in hull design as everything else.
 
maxhopper502 said:
My boat looks like it would be a perfect candidate for the batwings and this is the first I have ever heard of them.
I was going to put paravanes on and I still could at a later date but am now thinking when she goes on the slip in march I will fit batwings.
Google is not telling me much on the dimensions needed to be effective, has anyone got any advice on what I may need?
I am thinking 2.4m (8 feet) Wide keeping it about 20 cm inside the boat and maybe 3m (10 feet) long and using either 12mm or 16mm plate.
She is 65 feet long and about 90t.
Any advice is welcome.
CheersIMG_1923.jpg
Click to expand...
 
Looking good, max.

Keep us informed on how they perform in the rough.
 
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